Cycle oils such as LCCO produced in fluidized catalytic cracking (“FCC”) reactions contain two-ring aromatic species such as naphthalene. The need for blendstocks for forming low emissions fuels has created an increased demand for FCC products that contain a diminished concentration of multi-ring aromatics. There is also an increased demand for FCC products containing light olefins that may be separated for use in alkylation, oligomerization, polymerization, and MTBE and ETBE synthesis processes. There is a particular need for low emissions, high octane FCC products having an increased concentration of C2 to C4 olefins and a reduced concentration of multi-ring aromatics and olefins of higher molecular weight.
A high octane gasoline may be formed conventionally by hydrotreating an FCC cycle oil and then re-cracking hydrotreated cycle oil. The hydrotreated cycle oil may be recycled to the FCC unit from which it was derived, or it may be re-cracked in an additional catalytic cracking unit.
In such conventional processes, hydrotreating a cycle oil such as LCCO results in partial saturation of bicyclic hydrocarbon species such as naphthalene to produce tetrahydronaphthalene and alkyl-substituted derivatives thereof, collectively referred to herein as tetralins. The hydrotreating is performed under conditions that result in partially saturating the cycle oil's aromatic species. For example, in one conventional process a cycle oil containing naphthalene as the most abundant aromatic species is hydrotreated under relatively mild conditions so that tetralins are the most abundant aromatic species in the hydrotreated product.
Unfortunately, re-cracking the hydrotreated cycle oil in accordance with the conventional processes results in undesirable hydrogen transfer reactions that convert partially saturated species such as tetralins into polynuclear aromatics such as naphthalene.
There remains a need, therefore, for new processes for forming naphtha and olefin from hydrotreated cycle oils such as LCCO.